Economics is not an exact science.

Mainstream economics scholarship produces theory without facts ("pure theory") and facts without theory ("applied economics")

In spite of all the foregoing, there is a science of economics, a true, and even exact, science, which reaches laws as universal as those of mathematics and mechanics. The greatest need for the development of economics as a growing body of thought and practice is an adequate appreciation of the meaning, and the limitations, of this body of accurate premises and rigorously established conclusions. It comes about in the same general way as all science, except perhaps in a higher degree, i.e., through abstraction. There are no laws regarding the content of economic behavior, but there are laws universally valid as to its form. There is an abstract rationale of all conduct which is rational at alt, and a rationale of all social relations arising through the organization of rational activity.

Economics is in high degree a pedagogical discipline, and an economist must be in close touch with popular psychology in order to know what ought to be said at any particular moment.

Economic theory is the most prestigious subject of instruction and study. Agricultural economics, labor economics and marketing are lower caste fields of study.

[E]conomics can never be a science in the sense that physics or chemistry is. There are many different types of economic theory, each emphasizing different aspects of a complex reality, making different moral and political value judgments and drawing different conclusions. ...[E]conomic theories constantly fail to predict real-world developments... not least because human beings have... free will, unlike chemical molecules or [other] physical objects.

Economics is a social science, not a physical science.

Economics is a science of thinking in terms of models joined to the art of choosing models which are relevant to the contemporary world. It is compelled to be this, because, unlike the typical natural science, the material to which it is applied is, in too many respects, not homogeneous through time. The object of a model is to segregate the semi-permanent or relatively constant factors from those which are transitory or fluctuating so as to develop a logical way of thinking about the latter, and of understanding the time sequences to which they give rise in particular cases.
Good economists are scarce because the gift for using "vigilant observation" to choose good models, although it does not require a highly specialised intellectual technique, appears to be a very rare one.

The economist studies the disposal of scarce means. He is interested in the way different degrees of scarcity of different goods give rise to different ratios of valuation between them, and he is interested in the way in which changes in conditions of scarcity, whether coming from changes in ends or changes in means—from the demand side or the supply side—affect these ratios. Economics is a science which studies human behavior as a relationship between ends and scarce means which have alternative uses.

Modern economics is “sick”. Economics has increasingly become an intellectual game played for its own sake and not for its practical consequences. Economists have gradually converted the subject into a sort of social mathematics in which analytical rigor as understood in math departments is everything and empirical relevance (as understood in physics departments) is nothing. If a topic cannot be tackled by formal modelling, it is simply consigned to the intellectual underworld. To pick up a copy of American Economic Review or Economic Journal, not to mention Econometrica or Review of Economic Studies these days is to wonder whether one has landed on a strange planet in which tedium is the deliberate objective of professional publication. Economics was condemned a century ago as “the dismal science”, but the dismal science of yesterday was a lot less dismal than the soporific scholasticism of today.

Well, I will say this. And this is the main thing to remember. Macroeconomics -- even with all of our computers and with all of our information -- is not an exact science and is incapable of being an exact science. It can be better or it can be worse, but there isn't guaranteed predictability in these matters.

If it were not for the hope that a scientific study of men's social actions may lead, not necessarily directly or immediately, but at some time and in some way, to practical results in social improvement, not a few students of these actions would regard the time devoted to their study as time misspent. That is true of all social sciences, but especially true of economics. For economics "is a study of mankind in the ordinary business of life"; and it is not in the ordinary business of life that mankind is most interesting or inspiring.

You will perceive that economy, scientifically speaking, is a very contracted science; it is in fact a sort of vague mathematics which calculates the causes and effects of man's industry, and shows how it may be best applied. There are a multitude of allied branches of knowledge connected with mans condition; the relation of these to political economy is analogous to the connexion of mechanics, astronomy, optics, sound, heat, and every other branch more or less of physical science, with pure mathematics.

There is much evidence that people are not rational, in the economist’s sense; nor do they take into account expectation, in the precise interpretation of that word. As a result economic theory often does not correspond with what happens in the market. Some would argue that we need descriptive economics. I would argue that all should be taught about probability, utility, and MEU (maximization of expected utility) and act accordingly.